Field of the Invention
The present invention relates to a sheet feeding apparatus, which is configured to feed a sheet, and an image forming apparatus.
Description of the Related Art
In general, an image forming apparatus, such as a printer, a copying machine, or a facsimile machine, includes a sheet feeding apparatus configured to feed a sheet to an image forming unit. There is given such sheet feeding apparatus configured to stack a sheet on a stacking tray that is arranged in a sheet receiving unit and is capable of being raised and lowered, raise the stacking tray to a position at which the sheet can be fed, and then deliver the sheet to the image forming unit by a feeding unit (see Japanese Patent Application Laid-Open No. 2011-136811). In such sheet feeding apparatus, the sheet receiving unit is configured to be mountable to and drawable from a main body of the sheet feeding apparatus so that sheets can easily be stacked on the sheet receiving unit during stacking of sheets. Further, the stacking tray is lowered to a predetermined sheet stacking position in conjunction with the drawing operation.
The sheet feeding apparatus which employs a raising and lowering system in the related art has the following configuration. When a sheet bundle stacked on the stacking tray is raised, an uppermost sheet of the sheet bundle is brought into abutment against a pickup roller. When the pickup roller is rotated, a flag unit arranged on a roller holder (hereinafter referred to as “feeding unit”) moves to respond to a sensor. With this configuration, even when floating, warpage, and the like occur in the sheets during stacking of the sheets, the uppermost sheet can be detected accurately at a pickup position. Thus, a pickup operation (feeding operation) can be performed accurately.
However, according to the configuration of Japanese Patent Application Laid-Open No. 2011-136811, when the raising operation of the stacking tray is started under the condition that the feeding unit is not mounted, for example, under the condition that a user has forgotten to mount the feeding unit which has been removed temporarily at a time of roller replacement, a signal for stopping the raising operation cannot be detected. In such case, the stacking tray may be raised to a position higher than a prescribed level to damage surrounding constituent portions or cause trouble such as jam (paper jam). Further, even when the stacking tray does not damage the surrounding constituent portions, the following problem may arise. When the user performs printing in this state, the sheet is not fed, and jam is determined. As a result, it is difficult for the user to notice that the jam has been caused by the absence of a roller.